Well for one thing it looks like a very poorly designed circuit. It appears to be a full wave bridge rectifier circuit that has poor protection. Increase the PIV (Positive Inverse Voltage) of whatever the rectifiers are rated at. Add MOV protection to the DC and the AC. If there is any room to mount a commercial full wave bridge to metal for heat sink and solder wires on board to run to the commercial bridge. MOV's can be installed on the externally mounted bridge if possible. Make the MOV's 100 volts higher then working voltages. Inductive kick from inductive sources may be blowing rectifiers. As an example an OTIS 6164BP relay puts out 16,000 volts of inductive kick for a couple nano-seconds. This will eventually rupture silicon rectifiers and cause failure without MOV protection. (Metal Oxide Varister)